Does Doxycycline make cats thirsty? Also cat losing weight but always hungry

Does anyone know if Doxycycline can cause increased thirst in cats? I've been googling it but not finding alot of info. The vet prescribed it for my cats George and Oliver for a cough that we haven't been able to figure out. George had previously tested positive for mycoplasma 1.5 years ago after a PCR test and because these two guys are roomies and were both coughing, they were both prescribed Doxy. It worked after 3 weeks of treatment but then returned about half a year later. The vet prescribed it again and the cough went away but then they both started coughing again a few months later. So when we moved, I brought both cats into another vet about 2 weeks ago who did a blood serum PCR test on each cat instead of a throat swab PCR test that was done on George a year and a half earlier. Both boys were negative. But they are both couging. Not alot but it's the same cough they've always had and they strain their necks out and the cough sounds wet and never produces anything (no hairball, nothing). So the vet prescribed more Doxy because it has worked the last few times but this time she's got them on it for 4 weeks. We are just at the 2 week mark and they are going through so much water!! The two of them seem to be drinking a few cups a day which is much more than usual. I don't know if one is drinking more than the other and will try to see if I can determine that. I'm concerned about possible kidney issues. Unfortunately since the bill for both George and Ollie was over 500.00 for exams, blood work and meds, I chose to just have them do CBC's and T4 for Ollie because I was worried he might be hyperthyroid and the PCR on the cats and didn't pay the extra 60.00 per cat to have the full geriatric panel done which I should have!! It would have indicated if either of them was dealing with a kidney issue in which case Doxy is not the best idea. The thyroid test for Oliver came back as normal.

But, I'm wondering if anyone else has any experience with Doxycycline and if it made their cats more thirsty? And if you have any ideas about why Ollie is losing weight and getting quite thin but always hungry and eats alot and has this darned cough that the vets can't seem to figure out.

I'm also worried about diabetes. I will call the vet to see if there would have been a glucose reading in the test they did. I'm not sure. The vet just said that everything looked normal.
p.s. I just treated them both with Strongid in case the coughing could be roundworm although there has been no evidence of worms in the box.

Increased thirst and hunger with little to no weight gain (or sometimes weight loss) is the poster child cat for hyperthyroidism. I strongly recommend you take them to the vet to have bloodwork ran to check for that among other metabolic issues and health diseases (diabetes, thyroid, and kidney disease typically can all be checked with the same panel).

He had a t-4 add on test 2 weeks ago to check his thyroid function and the vet said that came back as normal. But I he didn't have the full geriatric panel done so I will probably end up doing that to see how his organs are functioning. Hoping for the best.

All of my cats were put on doxycycline for 1 month because my 3 kittens brought chlamydia with them and eye drops alone just didn't work. I never noticed that any of them were drinking more water but I did notice that some of them didn't want to eat as much food as they usually do.

Last year my cats Alani & Blaze had coughs and I never knew what caused it. My vet diagnosed them with a laryngeal infection. At the time I had 4 other cats too but none of them got sick. Here's the thread about it: http://petoftheday.com/talk/showthre...-Update-2-5-12. I hope that you'll be able to find out what's causing this. Do you think it could be heartworms?

All of my cats were put on doxycycline for 1 month because my 3 kittens brought chlamydia with them and eye drops alone just didn't work. I never noticed that any of them were drinking more water but I did notice that some of them didn't want to eat as much food as they usually do.

Last year my cats Alani & Blaze had coughs and I never knew what caused it. My vet diagnosed them with a laryngeal infection. At the time I had 4 other cats too but none of them got sick. Here's the thread about it: http://petoftheday.com/talk/showthre...-Update-2-5-12. I hope that you'll be able to find out what's causing this. Do you think it could be heartworms?

Doxy is an antibiotic and, like most antibiotics, may cause some tummy/GI upset, which presents itself as inappetance in milder cases

Heartworms are pretty uncommon in cats, but it only takes one to three adult heartworms to be fatal to a cat. Your best diagnostic step to determine this is xrays. Many cats with heartworms are commonly misdiagnosed with feline asthma. Sadly, there is no safe and effective method of treating feline heartworms. As I said, it isn't very common though.